PHOTOTROPHIC GROWTH AND CHLOROSOME FORMATION IN CHLOROFLEXUS-AURANTIACUS UNDER CONDITIONS OF CAROTENOID DEFICIENCY

Chloroflexus aurantiacus was grown phototrophically in the presence of 60 mu g of 2-hydroxybiphenyl (HBP) per ml, which inhibited the format ion of colored carotenoids up to about 90%, while bacteriochlorophyll (BChl) c formation and phototrophic growth were not significantly infl uenced. When the HBP concentration was increased, the latter two proce sses became inhibited, yet, no further inhibition of carotenoid format ion was possible. The typical shape of chlorosomes was not affected af ter growth in the presence of 60 mu g of HBP per mi. However, the chlo rosome dimensions were slightly decreased. Chlorosome preparations fro m carotenoid-deficient cultures lacked significant amounts of colored carotenoids and exhibited lower buoyant densities than chlorosomes fro m uninhibited control cultures. As compared on a BChl c basis, the rel ative contents of the two larger chlorosomal polypeptides of 10.8 and 15.5 kDa (apparent M-r = 11000 and 18000) were not affected by HBP, wh ile formation of the 5.7 kDa (M-r = 3700) polypeptide was inhibited by 50%. The data suggest that, in C. aurantiacus, colored carotenoids ar e largely dispensable for phototrophic growth and chlorosome formation . Moreover, chlorosome formation and BChl c incorporation into chloros omes in the absence of about half of the regular amount of the 5.7 kDa polypeptide excludes a constant relationship between these parameters .